Other than flat tires, one of the most frequent "breakdowns" while bicycling is the result of broken spokes. In conventional bicycle wheels, spokes hook through holes in the hubs in a variety of lacing patterns with some spokes fed from outside the hub and others fed from inside the hub. The spokes are then tensioned by adjustment of the spoke nipples in the rim to center the rim on the hub. While a blow to the spoke near the rim may break the spoke, the most common breaking point is at the elbow where the spoke bends at the hub. It is well known that bends in metal create stress points and this stress clearly is evident in spoke breakage.
The trend in bicycle wheels is to decrease wind drag by any means possible. While disk wheels and tri-spoke wheels are available to minimize the drag surfaces, their prices can be prohibitive for the average bicyclist. An alternative to these specialized wheels is to use fewer standard spokes. This, however, introduces even greater risk of spoke breakage and distortion of the rim if a spoke breaks.
A number of patents have been issued for hub and spoke assemblies for wheels that are intended to improve the means for attaching the spokes to the hub. While a few are addressed specifically toward bicycle wheels, most claim to be applicable to any type of spoked wheel without recognizing the special requirements involved with bicycle wheels. Specifically, bicycle wheels are much lighter weight than spoked wheels for motor vehicles (cars, trucks, motorcycles) or wagon wheels, since the construction of these latter wheels does not usually need to address how much weight the wheels add to the total weight of the vehicle. Thus, large gauge wires can be used to guard against breakage. Further, the ratio of the spoke length to the rim or hub width is much greater on a bicycle than on, for example, a car wheel, so the stress on the bicycle spokes is proportionally greater, The problem of strain on the spokes becomes even more pronounced with ultra-lightweight materials from which the elite types of bicycles and components are made, such as carbon, graphite, titanium, etc.
In Austrian patent number 37087, issued Apr. 26, 1909, a method for attaching the spokes to the hub of a child's wagon wheel describes treatment for the threaded end of the spokes which attaches to the hub in order to avoid corrosion of the spokes within the hub. This method simply involves making the threaded portion of the spoke long enough to span the thickness of the hub wall, but not so long as to extend into the cavity at the center of the hub. The issues addressed are entirely separate from the concerns in constructing a bicycle wheel, and there is no recognition of a special way that the spokes must extend radially from the hub to minimize breakage.
German patent number 62733, issued Jul. 26, 1891, discloses ball bearings for bicycle wheels, but is of interest for the way in which the spokes are attached to the hub. Specifically, the spokes are screwed into the hub in such a way that they bend at the point of exit from the hub flange, which is apparent from the Figures. This bend is the point of highest stress on the spoke, and if, this configuration were attempted with the lightweight spokes on today's bicycles, the spokes would break as soon as any weight was placed on the wheel.
Configurations similar to the above German patent are found in U.S. Pat. Nos. 278,534 of Gideon (issued May 29, 1883), 473,837 of Green (Apr. 26, 1892), 726,557 of Mesnard (Apr. 28, 1903) and 792,725 of Newton (Jun. 20, 1905). Each of these patents describe, among other things, spokes which are threaded to be screwed into corresponding threaded holes in the hub flanges. However, none of these inventions recognizes a problem with or addresses the issue of stress on the spokes at the point of exit from the hub when the spokes are thin and relatively lightweight. If these wheels were at all successful, they were so because the spokes were so heavy that they could bear the stress without breaking.
In spite of the number of patents which disclose threaded spokes which screw into the hub, current bicycle wheels rely exclusively on a spoke design in which the inner end of the spoke is bent in a hook shape and threaded through an opening in the hub. It is clear that the threaded spoke configuration as taught by the prior art has failed to supplant the hooked spoke design in spite of the many drawbacks of the latter design. This failure is due to the lack of recognition of the critical role that built-in stresses plays on the wheel assembly.